## Contact Angle and Wettability

EXAIR has been selling high-efficiency, hard-hitting compressed air products since 1983 for the purpose of drying and cleaning materials with compressed air.  The laminar airflow allows for a consistent force in the same direction, which is beneficial for effective cleaning and drying.  If we look closer at the surface of the material and how liquids interact, we can get a better understanding.

First, let’s look at the atoms of a solid.  Since the atoms are tightly packed and arranged in a stable format, the forces are even around each atom, except for the atoms on the outside surface.  These forces are unequal, so they will generate an imbalance, which is called surface tension.  This surface tension will have an atomic interface with other objects.  Let’s look at a liquid.  Liquid is a substance that flows readily.  Since it can flow, the surface tension on the outside will create a sphere in space.  So, what happens when these two surfaces interact?

If we look at a liquid, we can place a drop on a solid surface.  If the surface tension of the solid is weaker than the surface tension of the liquid, then the liquid will bead up.  If the solid has a strong surface tension compared to the liquid’s surface tension, then it will lay flat or wet out.  This phenomenon is important to know if you want things like liquids to wet out with inks and paints versus having the liquid bead up with waterproof materials.

We can measure how much force the solid surface is exerting when interacting with the liquid by the contact angle (refer to the photo above).   This angle will indicate the wettability of the fluid.  For a contact angle greater than 90o, the surface would be considered non-wettable with that liquid.  If the contact angle is less than 90o, then the liquid will wet out onto the surface.  For water, we have a variety of degrees of interaction as related to contact angles:

• >150o – Super-hydrophobic
• 90o – 150o – hydrophobic
• 30o – 90o – normal wetting
• 10o – 30o – hydrophilic
• <10o – Super-hydrophilic

Why is this important to know?  For drying and cleaning applications, it is beneficial to know how easy or difficult the liquid is to remove from the material.  If the contact angle is greater than 90o, then we can help the customer adjust the blowing angle and reduce the air pressure to save money because the liquid is easy to remove.  If the contact angle is less than 90o, then we can adjust the angle to be more direct as well as increase the force level to increase effectiveness.

How does this apply to EXAIR products?  We are the market leaders for non-contact drying and cleaning.  For applications where you need to remove as much water as possible for quicker heating cycles, to reduce labor costs when cleaning parts, or to quickly dry surfaces for labels and print quality, EXAIR has a variety of blow-off products; like the Super Air Knife.  Within these product lines, we offer a kit that includes a regulator and a shim set to vary the force levels to tackle the different degrees of wettability.  EXAIR is a proponent of using the least amount of air to “do the job”.  The regulator can make fine adjustments to the force levels while the shims will make a coarse adjustment.  So, depending on the contact angles, you can “dial in” the correct amount of force to clean and dry your products.  What could be better than this?  For U.S. and Canadian customers, EXAIR offers a 30-day unconditional guarantee on our cataloged items to try them out.  You can see for yourself how effective and efficient our products are.  If you would like to speak to an Application Engineer about your drying or cleaning application, we would be happy to make a recommendation to help solve your issues.

John Ball
Application Engineer
Email: johnball@exair.com

## EXAIR’s Super Air Knife Removes Moisture From Plastic Bottles Prior to Labeling

EXAIR’s Super Air Knife is THE best solution for compressed air blowoff operations that require a wide sheet of compressed air. We’ve been manufacturing Air Knives for over 35 years, with the Super Air Knife making its first appearance back in 1997. Since then, the Super Air Knife has undergone a few enhancements over the years as we’re constantly trying to not only introduce new products but also improve on the ones we have. We’ve added new materials, longer single piece knives, as well as additional accessories. But, by and large, the basic design has remained the same. As the saying goes: “If it ain’t broke, don’t fix it!”.

The Super Air Knife utilizes a source of compressed air to create a laminar sheet of high velocity air. This supplied compressed air mixes with ambient air that is entrained into the primary airstream. The Super Air Knife entrains ambient air at a rate of 40:1, making it VERY effective in a variety of drying, cleaning, and cooling applications. Available in lengths ranging from 3”-108” and in a variety of different materials of construction, there’s a Super Air Knife available for just about any application.

Any time you have product moving along a conveyor that needs to be cleaned, dried, or cooled off, a Super Air Knife is the ideal fit. I recently worked with our Argentinian Distributor on an application involving drying off plastic bottles just prior to applying a label to the outside. After the bottles are molded, they go through a washing operation to remove contaminants from the inside and outside of the bottles before they’re filled. After filling, a label must be applied to the outside of the bottle. Before installation of the Super Air Knives, they were allowing the bottles to air dry. As they moved along the conveyor, most of the residual water did come off and wasn’t causing any issues.

They were looking to increase production rates so that they could keep up with demand, however when they increased the speed of the conveyor there was still a good amount of residual water remaining on the bottles. This prevents the label from adhering properly to the outside of the bottle. Not only did this result in an added step to inspect the bottles, but those that weren’t labeled properly had to have the label removed and cleaned off before a new one could be put on. This actually ended up being less productive than just running the conveyor at a slower speed.

They came across the EXAIR Super Air Knife and decided to try (2) 110036 aluminum Super Air Knives to remove excess moisture just prior to labeling. The plant handles a wide variety of different sized bottles, so they also utilized the Universal Mounting System so that they could easily adjust the positioning of the knife based on the job. With the Super Air Knives in place, they were able to effectively run the operation nearly 20% faster without any problems.

With the quiet and efficient Super Air Knives in place, they were able to increase production rates in order to fulfill their orders on time. If there’s an application in your facility that could necessitate the use of an EXAIR Super Air Knife, give us a call. With 16 different lengths available from stock in 4 different materials, same day shipping with orders placed by 3:00 ET, AND our unconditional 30 day guarantee, there’s no excuse not to give one a try!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com